‘The day when a sportsman … lets considerations of vanity or interest take over, on this day his ideal will die.” So remarked Pierre de Coubertin, who founded the modern Olympic Games in 1896. We’ll never know what he would have made of the practice among some current athletes to post sponsored tweets, but we can safely assume he would have disapproved. The Office of Fair Trading is said to be equally disapproving of celebrities who tweet positively about their sponsors, without revealing to their followers that such a commercial relationship exists. And some Olympic coaches have also expressed concern that such activities are a distraction when the focus should be solely on training.

But this hasn’t stopped some athletes from using Twitter to name their sponsors. High-profile Olympians such as Tom Daley and Rebecca Adlington have both tweeted about cars they have been lent by BMW. Adlington, a swimmer, has also tweeted about “some amazing Elizabeth Arden products” – “very needed as the chlorine is killing my skin”.

What is the commercial value to the sponsor of such a tweet? Alex Kemmis Betty, an account executive at Professional Sports Group, representing Daley, says the industry has not yet formulated rates for sponsors willing to pay for a tweet from a celebrity. “Most contracts have a social media element, but it’s difficult to value it. This will happen – just as is the case now with how many ‘appearance days’ they must give their sponsor. Many [clients] post tweets about their sponsors out of loyalty or gratitude. Sometimes a sponsor will send them a weblink and ask them to tweet it. But we also advise the athletes to ‘keep it real’ and not to over do it.”

Mike Essex, of London-based digital agency Koozai, says that software is being used to assess a tweeter’s influence, monitoring “retweets, mentions, links, use of photographs, etc. All this will go into building a metric for the industry.Sponsored tweets don’t always work, though; McDonald’s tried to get the hashtag #McdStories going, but it ended up only attracting negative comments.” But some sites already value celebrity tweets. In the US, SponsoredTweets.com’s rate card claims that one sponsored tweet by Jamie Oliver (2.1m followers) would cost an advertiser $3,250.